Abstract
A previously unknown maltose transporter is essential for the conversion of starch to sucrose in Arabidopsis leaves at night. The transporter was identified by isolating two allelic mutants with high starch levels and very high maltose, an intermediate of starch breakdown. The mutations affect a gene of previously unknown function, MEX1. We show that MEX1is a maltose transporter that is unrelated to other sugar transporters. The severe mex1 phenotype demonstrates that MEX1is the predominant route of carbohydrate export from chloroplasts at night. Homologous genes in plants including rice and potato indicate that maltose export is of widespread significance.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Sequence
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Arabidopsis / genetics
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Arabidopsis / metabolism*
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Arabidopsis Proteins / chemistry
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Arabidopsis Proteins / genetics
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Arabidopsis Proteins / metabolism*
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Biological Transport
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Chloroplasts / metabolism
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Cloning, Molecular
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Crosses, Genetic
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DNA, Complementary
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Genes, Plant
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Glucose / metabolism
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Maltose / metabolism*
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Molecular Sequence Data
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Monosaccharide Transport Proteins / chemistry
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Monosaccharide Transport Proteins / genetics
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Monosaccharide Transport Proteins / metabolism*
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Mutation
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Phenotype
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Plant Leaves / metabolism*
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Recombinant Fusion Proteins / metabolism
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Sequence Alignment
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Starch / metabolism*
Substances
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Arabidopsis Proteins
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DNA, Complementary
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Monosaccharide Transport Proteins
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Recombinant Fusion Proteins
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Maltose
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Starch
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Glucose